Prosthetic heart valve with upper and lower skirts

ABSTRACT

A prosthetic valve structure, for use at a native atrioventricular heart valve, includes a frame, prosthetic leaflets, an upper skirt, and a lower skirt. The frame circumscribes a longitudinal axis of the structure. The leaflets are configured to facilitate upstream-to-downstream bloodflow through the structure. The upper skirt has an upstream perimeter. The lower skirt is downstream of the upper skirt, and has a downstream perimeter. The upper skirt extends away from the lower skirt, in an upstream direction and radially outward toward the upstream perimeter. The lower skirt extends away from the upper skirt, in a downstream direction and radially outward toward the downstream perimeter. A downstream portion of the frame is disposed downstream of at least part of the downstream perimeter of the lower skirt.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a Continuation of U.S. Ser. No. 16/532,945 toHaCohen, filed Aug. 6, 2019, and entitled “PROSTHETIC HEART VALVE WITHUPPER SKIRT,” which is a Continuation of U.S. Ser. No. 16/388,038 toHaCohen, filed Apr. 18, 2019, and entitled “ROTATION-BASED ANCHORING OFAN IMPLANT” (now U.S. Pat. No. 10,548,726), which is a Continuation ofU.S. Ser. No. 16/183,140 to HaCohen, filed Nov. 7, 2018, and entitled“FOLDING RING PROSTHETIC HEART VALVE,” which published as US2019/0069998, and which is a Divisional of U.S. Ser. No. 15/188,507 toHaCohen, filed Jun. 21, 2016, and entitled “FOLDING RING IMPLANT FORHEART VALVE,” which published as US 2016/0296330 (now U.S. Pat. No.10,231,831), and which is a Continuation of U.S. Ser. No. 14/522,987 toHaCohen, filed Oct. 24, 2014, and entitled “IMPLANT FOR ROTATION-BASEDANCHORING,” which published as US 2015/0045880 (abandoned), and which isa Continuation of U.S. Ser. No. 12/961,721 to HaCohen, filed Dec. 7,2010, and entitled “ROTATION-BASED ANCHORING OF AN IMPLANT,” whichpublished as 2011/0137410 (now U.S. Pat. No. 8,870,950), which claimsthe benefit of U.S. Provisional Patent Application 61/283,819, entitled“FOLDABLE HINGED PROSTHETIC HEART VALVE,” to Hacohen, filed Dec. 8,2009, which is incorporated herein by reference.

FIELD OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention relates in general to valvereplacement. More specifically, embodiments of the present inventionrelate to replacement of an atrioventricular valve and prosthetic valvetherefor.

BACKGROUND

Ischemic heart disease causes regurgitation of a heart valve by thecombination of ischemic dysfunction of the papillary muscles, and thedilatation of the ventricle that is present in ischemic heart disease,with the subsequent displacement of the papillary muscles and thedilatation of the valve annulus.

Dilation of the annulus of the valve prevents the valve leaflets fromfully coapting when the valve is closed. Regurgitation of blood from theventricle into the atrium results in increased total stroke volume anddecreased cardiac output, and ultimate weakening of the ventriclesecondary to a volume overload and a pressure overload of the atrium.

SUMMARY OF EMBODIMENTS

In some applications of the present invention, a prosthetic heart valvestructure is provided that collapses and expands by means of one or morevalve pivot joints. The prosthetic valve structure is typicallydesignated for implantation in a native atrioventricular valve site of aheart of a patient, although for some applications, the prosthetic valvestructure is designated for implantation at the aortic or tricuspidvalve. The prosthetic valve structure comprises an annular ring portionthat is designated for placement adjacent to the ventricular surface ofthe native valve of the patient. This annular ring portion comprises thevalve pivot joints, which facilitate collapsing of the prosthetic valvestructure for transcatheter advancement of the valve toward the heart ofthe patient. Additionally, the annular portion of the prosthetic valvestructure is coupled to a plurality of anchors which are configured tograsp the native chordae tendineae of the heart of the patient. Theseanchors comprise generally curved prong structures which, in an expandedstate of the prosthetic valve structure, are aligned circumferentiallyalong the annular ring portion of the prosthetic valve structure(generally perpendicular to a radius of the annular ring portion). Oncethe annular ring portion is positioned adjacent to the ventricularsurface of the native mitral valve, the prosthetic valve structure isrotated, in order for the anchors to engage the native chordaetendineae. During the engaging, portions of the native chordae tendineaeare gathered between each anchor and a respective portion of the annularring. This engaging provides support to the prosthetic valve structureas it is positioned in and replaces the native valve. Additionally, theprosthetic valve structure comprises ventricular and atrial skirts whichprovide flush positioning of the prosthetic valve in the native valve.

There is therefore provided, in accordance with some applications of thepresent invention, apparatus for use with a prosthetic valve that isdesignated for implantation at a native heart valve of a patient,including:

a valve ring having a plurality of ring segments, each of the segmentsbeing hingedly coupled to at least one adjacent segment at a pivotjoint,

the valve ring being configured:

-   -   to be placed adjacent to a surface of the native heart valve,        the prosthetic valve having been coupled to the valve ring,    -   in an expanded state thereof, to define a ring, all of the pivot        joints being disposed in a plane that is perpendicular to a        longitudinal axis of the ring, and    -   to be foldable from the expanded state into a shape that has a        generally circular cross-section that defines and surrounds at        least in part a central lumen, by folding the segments with        respect to each other, at the pivot joints.

For some applications, the segments of the ring are configured to becomeat least partially twisted due to the ring being folded from theexpanded state.

For some applications, the prosthetic valve includes a trileaflet valve,and the ring has a number of ring segments that is a multiple of six.

For some applications, the ring has exactly six segments.

For some applications, the prosthetic valve includes a bileaflet valve,and the ring has a number of ring segments that is a multiple of four.

For some applications, the ring has exactly four segments.

There is further provided, in accordance with some applications of thepresent invention, a method for use with a prosthetic valve that isdesignated for implantation at a native heart valve of a patient,including:

placing in a vicinity a surface of the native heart valve, a valve ringthat is coupled to the valve, while the valve ring is in a folded statethereof,

-   -   the ring having a plurality of ring segments, each of the        segments being hingedly coupled to at least one adjacent segment        at a pivot joint,    -   in the folded state thereof, the ring having a shape that has a        generally circular cross-section that defines and surrounds at        least in part a central lumen;

expanding the ring such that all of the pivot joints become disposed ina plane that is perpendicular to a longitudinal axis of the ring, byapplying a force to at least some of the pivot joints; and

when the ring is in an expanded state thereof, positioning the ringadjacent to a surface of the native valve.

For some applications, applying the force to some of the pivot jointsincludes pushing on pivot joints that are disposed on a proximal side ofthe ring, while the ring is in the folded state thereof.

For some applications, the native valve includes a native mitral valve,and positioning the ring adjacent to the surface of the valve includespositioning the ring adjacent to a ventricular surface of the nativemitral valve.

There is additionally provided, in accordance with some applications ofthe present invention, apparatus for use with a prosthetic valve that isdesignated for implantation at a native mitral valve of a patient,including:

an annular ring configured to be placed at a ventricular surface of thenative mitral valve, the prosthetic valve having been coupled to theannular ring; and

at least one anchor disposed circumferentially with respect to theannular ring so as to define a space between the anchor and the annularring.

For some applications, the anchor is configured to grasp a portion ofnative chordae tendineae of a heart of the patient by the annular ringbeing rotated.

For some applications, the annular ring is configured to be collapsible.

For some applications, the ring includes a plurality of ring segments,each of the segments being hingedly coupled to at least one adjacentsegment at a pivot joint, and the ring is configured to be collapsed byfolding the segments with respect to each other, at the pivot joints.

There is further provided, in accordance with some applications of thepresent invention, a method, including:

positioning an annular ring portion of a prosthetic valve structure at aventricular surface of a native heart valve of a patient; and

grasping a portion of native chordae tendineae of a heart of the patientby rotating the annular ring portion of the prosthetic valve structure.

In some applications of the present invention, grasping the portion ofthe native chordae tendineae includes facilitating placing the portionof the native chordae tendineae in a space between a segment of theannular ring portion and an anchor disposed circumferentially withrespect to the segment of the annular ring portion.

In some applications of the present invention, positioning the annularring portion includes:

transcatheterally advancing the prosthetic valve structure toward thenative valve of the patient in a collapsed state thereof; and

expanding the prosthetic valve structure from the collapsed state.

In some applications of the present invention, expanding the prostheticvalve structure includes pivoting a plurality of segments of the annularring portion at respective pivot joints that couple together adjacentsegments of the annular ring portion.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exploded view of a prostheticheart valve, in accordance with some applications of the presentinvention;

FIGS. 2A-B are schematic illustrations of the prosthetic heart valve ofFIG. 1 in an assembled, collapsed state, in accordance with someapplications of the present invention;

FIG. 3 is a schematic illustration of the prosthetic heart valve of FIG.1 in an assembled, expanded state, in accordance with some applicationsof the present invention; and

FIG. 4 is a schematic illustration of respective views of the prostheticheart valve of FIG. 1, while anchors of the valve are anchoring thevalve to chordae tendineae of a subject, in accordance with someapplications of the present invention.

The following figures, mutatis mutandis, originate from U.S. ProvisionalPatent Application 61/283,819 to HaCohen, which was incorporated byreference into the original specification of U.S. Ser. No. 12/961,721 toHaCohen:

FIG. 5 is a schematic illustration of an exploded view of a prostheticheart valve, in accordance with some applications of the presentinvention;

FIG. 6 is a schematic illustration of the prosthetic heart valve of FIG.5 in an assembled, expanded state, in accordance with some applicationsof the present invention; and

FIG. 7 is a schematic illustration of the prosthetic heart valve of FIG.5 in an assembled, collapsed state, in accordance with some applicationsof the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference is now made to FIGS. 1-4, which are schematic illustrations ofan expandable and collapsible prosthetic valve structure 20, inaccordance with some applications of the present invention. Theprosthetic valve structure is configured for implantation in andreplacement of a native atrioventricular valve of a patient. Typically,the prosthetic valve structure is configured for implantation in andreplacement of a native mitral valve of the patient.

The prosthetic valve structure comprises an annular valve ring 24, whichcomprises a plurality of curved metal segments 26 and a plurality ofpivot joints 30 which facilitate the collapsing and expanding of theprosthetic valve structure. The annular valve ring is typicallysurrounded by a valve ring fabric sleeve 34 comprising a braided mesh offabric, e.g., Dacron. This sleeve promotes fibrosis followingimplantation of the prosthetic valve structure in the native valve ofthe patient. The annular valve ring is coupled to a prosthetic valvethat includes a plurality of valve leaflets 44. The valve leaflets arecoupled to a flexible valve leaflet frame 40 (e.g., comprising nitinol,by way of illustration and not limitation), which is, in turn, coupledto a valve leaflet frame fabric 42. Typically, the valve leaflet framefabric (e.g., a fabric comprising Dacron) is coupled to (for example,sutured to) valve ring fabric sleeve 34.

For embodiments in which the prosthetic valve is designated to replacethe native mitral valve of the patient, the prosthetic valve comprisesthree artificial or tissue-based leaflets 44 a, 44 b, and 44 c (shown inFIG. 4), which are coupled to the inner perimeter of the annular valvering. For example, the leaflets may include pericardium, a polymer,and/or other materials, as would be obvious to one skilled in the art.

The annular valve ring portion of the prosthetic valve structure iscoupled: (1) at a first surface thereof to an upper skirt, whichcomprises an upper skirt fabric 38 coupled to a flexible upper skirtframe 36, and (2) at a second surface thereof to a lower skirt, whichcomprises a lower skirt fabric 48 coupled to a flexible lower skirtframe 46. Typically, the upper and lower frames comprise a flexiblematerial, e.g., nitinol by way of illustration and not limitation.Typically, when the prosthetic valve structure is implanted in theexpanded state, as shown in FIG. 4:

(a) the annular valve ring portion is configured to be disposed at aventricular surface of the native valve,

(b) the upper skirt is designated to rest against an atrial portion ofthe native mitral valve, and

(c) the lower skirt is designated to rest against a ventricular surfaceof the native valve and to push radially the native leaflets of thenative valve.

FIG. 1 shows components 22 of valve structure 20 in an exploded view.Each segment 26 of annular valve ring 24 is coupled at its respectiveends to respective ends of adjacent segments via a hinge. For example,as shown, the hinge may include a connecting element 28 that is insertedinto holes in the ends of the adjacent segments, such that the adjacentsegments form a pivot joint 30. The pivot joints of the ring portionenable the entire prosthetic valve structure to pivot into a collapsedstate, the collapsed state being shown in FIGS. 2A-B. Typically, thevalve comprises: (a) three “upper” valve pivot joints 30U (shown in FIG.2A) which are disposed at 120 degrees along the annular valve ring andare near the upper skirt frame 36, in the collapsed state of the valve,shown in FIG. 2A; and (b) three “lower” valve pivot joints 30L (shown inFIG. 2A) also disposed with a separation therebetween of 120 degrees,alternating with the upper valve pivot joints. The lower valve pivotjoints are near the lower skirt frame 46, in the collapsed state of thevalve as shown in FIG. 2A. The upper valve pivot joints are exposed at aproximal portion of the valve in the collapsed state of the valve (i.e.,adjacent to an upper skirt region of the prosthetic valve structure, asshown in FIG. 2A), such that a physician is able to push on the uppervalve pivot joints with a pushing tool, as described hereinbelow.Typically, when the ring is in its expanded state, all of the pivotjoints are disposed in a plane that is perpendicular to longitudinalaxis 10 of ring 24.

The pivot joints enable the prosthetic valve structure to collapse toform a shape having a generally circular cross-section that defines andsurrounds at least in part a central lumen 50, as shown in FIGS. 2A-B.Typically, the pivot joints enable the valve to assume an outer diameterof less than 10 mm, e.g., less than 6 mm (by way of illustration and notlimitation), in its collapsed state, as shown in FIG. 2A. Furthertypically, central lumen 50 (which is defined by ring 24 in itscollapsed state) has a cross-sectional length (e.g., diameter D, shownin FIG. 2B) of between 3 mm and 5 mm, the length being measured in aplane that is perpendicular to longitudinal axis 10 of the valve (shownin FIG. 1).

Typically, when used with a trileaflet valve, ring 24 includes sixsegments 26, such that there are a total of six pivot joints 30 (ofwhich three are upper pivot joints 30U, and three are lower pivot joints30L), and such that each of the leaflets is disposed between twoadjacent upper pivot joints 30U, or two adjacent lower pivot joints 30L.For some applications, the ring includes twelve (or another multiple ofsix) pivot joints, such that each of the leaflets of a trileaflet valveis disposed between two non-adjacent upper pivot joints 30U, or twonon-adjacent lower pivot joints 30L. For some applications, ring 24 isused with a bileaflet valve. For such applications, the ring may includefour, eight, or twelve segments 26, such that there are a correspondingnumber of pivot joints, and such that each of the leaflets is disposedbetween two of the upper pivot joints or two of the lower pivot joints.

Each of segments 26 of ring 24 is configured to become twisted when thering is folded, as shown in FIG. 2A. For some applications, due toshape-memory properties of the segments, the segments facilitate theexpansion of the ring, since the segments are pre-shaped in non-twistedshapes.

In the collapsed state of the valve, the valve leaflet frame, the valveleaflets, the upper skirt, and the lower skirt are also collapsed.Typically, the valve is configured such that the expansion of the ringcauses each of the aforementioned portions to become expandedautomatically.

In order to deploy prosthetic valve structure 20 inside the heart, thephysician pushes the upper pivot joints 30U distally, using a pushingtool. The pushing of the upper pivot joints enables annular valve ring24 to expand radially in order for the prosthetic valve structure toassume an expanded state, as shown in FIG. 3. Responsively to theexpanding of the prosthetic valve structure, valve leaflet frame 40,valve leaflets 44, upper skirt frame 36, and lower skirt frame 46 alsoexpand from their respective collapsed states.

For some applications, annular valve ring 24 is coupled to a pluralityof generally curved, prong-shaped anchors 32, for example, four to eightanchors, e.g., six anchors, as shown by way of illustration and notlimitation in FIG. 1. In the expanded state of valve structure 20, asshown in FIG. 3, the anchors are disposed circumferentially and inconcentric alignment with the annular valve ring. As shown in FIG. 3,the anchors project from the annular valve ring through the valve ringfabric sleeve 34. As the prosthetic valve structure transitions to acollapsed state, as shown in FIG. 2A, the anchors remain alongsiderespective segments of the annular valve ring to which each anchor isadjacently disposed in the expanded state of the prosthetic valvestructure.

During implantation of prosthetic valve structure 20, a lower portion ofthe prosthetic valve structure is first advanced toward the ventricularsurface of the native valve. Once the distal end of the catheter ispositioned in the ventricle of the patient, the physician pushesdistally on the upper valve pivot joints 30 in order to (1) exposeannular valve ring portion 24 and the lower skirt frame 46 and lowerskirt fabric 48 from within the catheter, and (2) in conjunction, expandthe annular valve ring. As the annular valve ring expands, lower skirtframe 46, valve leaflet frame 40, and valve leaflets 44 passively (i.e.,automatically) expand. As the physician expands the annular valve ring,each of the anchors remain disposed circumferentially with respect tothe segment of the annular valve ring to which the anchor is adjacentlydisposed (as shown in FIG. 3). In such a manner, a space is createdbetween each anchor and the respective segments of the annular valvering to which each anchor is adjacently disposed.

By pulling proximally on the catheter and the tool coupled to prostheticvalve structure 20 disposed therein, the annular valve ring ispositioned adjacent to a ventricular surface of the native valve. Oncethe valve ring portion is positioned adjacent to the ventricularsurface, the physician rotates annular valve ring 24 (e.g., by rotating30 degrees a tool coupled thereto) about an axis that runs between thenative valve from the atrium to the ventricle (which during implantationof the valve, is typically approximately aligned with longitudinal axis10 of the valve). During this rotation, portions of native chordaetendineae 60 are grasped and placed between each anchor and therespective segment of the annular valve ring to which the anchor isadjacently disposed, as shown in FIG. 4. This grasping of the leafletsprovides supplemental support to the prosthetic valve during andfollowing implantation thereof. Alternatively or additionally, supportis provided to the prosthetic valve by the upper and lower skirts,and/or by ring 24.

In conjunction with the grasping of the chordae tendineae, theprosthetic valve is secured in place. The physician then pulls thecatheter proximally in order to expose upper skirt frame 36 and upperskirt fabric 38 from within the catheter. The skirt then expands overthe atrial surface of the native valve in order to create a flushcoupling between the prosthetic valve and the native valve.

The following description, mutatis mutandis, originates from U.S.Provisional Patent Application 61/283,819 to HaCohen, which wasincorporated by reference into the original specification of U.S. Ser.No. 12/961,721 to HaCohen:

-   -   Reference is now made to FIGS. 5-7 which are schematic        illustrations of an expandable and collapsible prosthetic valve        100, in accordance with some applications of the present        invention. The prosthetic valve is configured for implantation        in and replacement of a native atrioventricular valve of a        patient. Typically, the prosthetic valve is configured for        implantation in and replacement of a native mitral valve of the        patient. The prosthetic valve comprises an annular valve ring        110 (as shown in the exploded view of FIG. 5), which comprises a        plurality of curved metal segments 112 and a plurality of pivot        joints 114 which facilitate the collapsing and expanding of the        prosthetic valve. The annular valve ring 110 is typically        surrounded by a valve ring fabric sleeve 116 comprising a        braided mesh of fabric, e.g., Dacron. This sleeve promotes        fibrosis following implantation of the prosthetic valve in the        native valve of the patient. The annular valve ring 110 is        coupled to a plurality of valve leaflets 120. The valve leaflets        are coupled to a flexible valve leaflet frame 122 (e.g.,        comprising nitinol by way of illustration and not limitation),        which is, in turn, coupled to a valve leaflet frame fabric 124.        Typically, the valve leaflet frame fabric (e.g., a fabric        comprising Dacron) is coupled to (for example, sutured to) the        valve ring fabric sleeve.    -   For embodiments in which the prosthetic valve is designated to        replace the native mitral valve of the patient, the prosthetic        valve comprises three artificial or tissue-based leaflets 120,        as shown, which are coupled to the inner perimeter of the        annular valve ring. It is to be noted that although these        leaflets are shown by way of illustration and not limitation, as        being a product of Neovasc Medical Ltd., the leaflets may        comprise any other leaflets known in the art.    -   The annular valve ring portion 110 of the prosthetic valve is        coupled: (1) at a first surface thereof to an upper skirt 140,        which comprises an upper skirt fabric 144 coupled to a flexible        upper skirt frame 142, and (2) at a second surface thereof to a        lower skirt 130, which comprises a lower skirt fabric 134        coupled to a flexible lower skirt frame 132. Typically, the        upper and lower frames comprise a flexible material, e.g.,        nitinol by way of illustration and not limitation. Typically,        when the prosthetic valve is implanted in the expanded state, as        shown in FIG. 6:    -   (a) the annular valve ring portion is configured to be disposed        at a ventricular surface of the native valve,    -   (b) the upper skirt is designated to rest against an atrial        portion of the native mitral valve, and    -   (c) the lower skirt is designated to rest against a ventricular        surface of the native valve and to push radially the native        leaflets of the native valve.    -   FIG. 5 shows the components of the valve in an exploded view.        Each segment 112 of the annular valve ring is coupled at its        respective ends to respective ends of adjacent segments via a        hinge, or a valve pivot joint 114. The pivot joints of the ring        portion enable the entire prosthetic valve to pivot into a        collapsed state, as shown in FIG. 7. Typically, the valve        comprises: (a) three “upper” valve pivot joints which are        disposed at 120 degrees along the annular valve ring and are        near the upper skirt frame, as shown in FIG. 7; and (b) three        “lower” valve pivot joints also disposed with a separation        therebetween of 120 degrees, alternating with the upper valve        pivot joints. The lower valve pivot joints are near the lower        skirt frame, as shown in FIG. 7). The upper valve pivot joints        are exposed at a proximal portion of the valve in a collapsed        state (i.e., adjacent to an upper skirt region of the prosthetic        valve, as shown in FIG. 7). The pivot joints enable the        prosthetic valve to assume a diameter of 6 mm (by way of        illustration and not limitation) in its collapsed state, as        shown in FIG. 7. In the collapsed state, the valve leaflet        frame, the valve leaflets, the upper skirt, and the lower skirt        are also collapsed.    -   In order to deploy the prosthetic valve inside the heart, the        physician distally pushes on the upper pivot joints using a        pushing tool. The pushing of the upper pivot joints enables the        annular valve ring to expand radially in order for the        prosthetic valve to assume an expanded state, as shown in        FIG. 6. Responsively to the expanding of the prosthetic valve,        the valve leaflet frame, the valve leaflets, the upper skirt,        and the lower skirt also expand from their respective collapsed        states.    -   The annular valve ring is coupled to a plurality of generally        curved, prong-shaped anchors 150, e.g., 6 as shown by way of        illustration and not limitation in FIG. 5. In an expanded state,        as shown in FIG. 6, the anchors are disposed circumferentially        and in concentric alignment with the annular valve ring. As        shown in FIG. 6, the anchors project from the annular valve ring        through the valve ring fabric sleeve. As the prosthetic valve        transitions to a collapsed state, as shown in FIG. 7, the        anchors remain alongside respective segments of the annular        valve ring to which each anchor is adjacently disposed in the        expanded state of the prosthetic valve.    -   During implantation of the prosthetic valve, a lower portion of        the prosthetic valve is first advanced toward the ventricular        surface of the native valve. Once the distal end of the catheter        is positioned in the ventricle of the patient, the physician        pushes distally on the upper valve pivot joints in order to (1)        expose the annular valve ring portion and the lower skirt from        within the catheter, and (2) in conjunction, expand the annular        valve ring. As the annular valve ring expands, the lower skirt,        the valve leaflet frame, and the valve leaflets passively        expand. As the physician expands the annular valve ring, each of        the anchors remain disposed circumferentially with respect to        the segment of the annular valve ring to which the anchor is        adjacently disposed (as shown in FIG. 6). In such a manner a        space is created between each anchor and the respective segments        of the annular valve ring to which each anchor is adjacently        disposed.    -   By pulling proximally on the catheter and the tool coupled to        the prosthetic valve disposed therein, the annular valve ring is        positioned adjacent to a ventricular surface of the native        valve. Once the valve ring portion is positioned adjacent to the        ventricular surface, the physician rotates the annular valve        ring (e.g., by rotating 30 degrees a tool coupled thereto) about        an axis that runs between the native valve from the atrium to        the ventricle. During this rotation, portions of the native        chordeae tendineae are grasped and placed between each anchor        and the respective segment of the annular valve ring to which        the anchor is adjacently disposed. This grasping of the leaflets        provides supplemental support to the prosthetic valve during and        following implantation thereof.    -   In conjunction with the grasping of the chordeae tendineae, the        prosthetic valve is secured in place. The physician then pulls        the catheter proximally in order to expose the upper skirt from        within the catheter. The skirt then expands over the atrial        surface of the native valve in order to create a flush coupling        between the prosthetic valve and the native valve.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1-17. (canceled)
 18. Apparatus for use at a native atrioventricularvalve of a heart of a subject, the apparatus comprising a prostheticvalve structure that comprises: a leaflet frame, circumscribing alongitudinal axis of the prosthetic valve structure; prostheticleaflets, coupled to the leaflet frame, and configured to facilitateupstream-to-downstream bloodflow longitudinally through the prostheticvalve structure; an upper skirt, having an upstream perimeter; and alower skirt, downstream of the upper skirt, and having a downstreamperimeter, wherein: (1) the upper skirt: extends away from the lowerskirt, in an upstream direction and radially outward toward the upstreamperimeter, and is configured to rest against an atrial surface of thenative atrioventricular valve, (2) the lower skirt: extends away fromthe upper skirt, in a downstream direction and radially outward towardthe downstream perimeter, and is configured to rest against aventricular surface of the native atrioventricular valve, and (3) adownstream portion of the leaflet frame is disposed downstream of atleast part of the downstream perimeter of the lower skirt.
 19. Theapparatus according to claim 18, wherein: the upper skirt comprises anupper skirt frame, and fabric coupled to the upper skirt frame; and thelower skirt comprises a lower skirt frame, and fabric coupled to thelower skirt frame.
 20. The apparatus according to claim 19, wherein thelower skirt frame has an outer edge that defines a wavy pathcircumferentially around the longitudinal axis, and that is disposedradially outward from the leaflet frame.
 21. The apparatus according toclaim 20, wherein the upper skirt frame has an outer edge that defines awavy path circumferentially around the longitudinal axis, and that isdisposed radially outward from the leaflet frame.
 22. The apparatusaccording to claim 21, wherein: the wavy path of the outer edge of theupper skirt frame defines alternating upper-skirt crests and upper-skirtdips, the upper-skirt crests being further from the longitudinal axisthan the upper-skirt dips, the wavy path of the outer edge of the lowerskirt frame defines alternating lower-skirt crests and lower-skirt dips,the lower-skirt crests being further from the longitudinal axis than thelower-skirt dips, and the alternating of the wavy path of the outer edgeof the lower skirt frame is out of phase with the alternating of thewavy path of the outer edge of the upper skirt frame.
 23. The apparatusaccording to claim 20, wherein the wavy path has a wavelength, andwherein the prosthetic valve structure is collapsible into a collapsedstate for transcatheter delivery to the heart, collapsing of theprosthetic valve structure into the collapsed state reducing thewavelength of the wavy path.
 24. The apparatus according to claim 19,wherein the upper skirt frame and the lower skirt frame both compriseNitinol.
 25. The apparatus according to claim 18, wherein the lowerskirt extends from the leaflet frame in a manner that defines a spacethat circumscribes the leaflet frame and is disposed between the leafletframe and the lower skirt.
 26. The apparatus according to claim 18,wherein: the prosthetic valve structure defines a narrowed waist on aplane that is perpendicular to the longitudinal axis, longitudinallybetween the upper skirt and the lower skirt; the prosthetic valvestructure further comprises joints, distributed circumferentially aroundthe longitudinal axis on the plane; and each of the joints comprises arespective connecting element that connects metallic segments of theprosthetic valve structure by being inserted into a respective hole ofthe prosthetic valve structure.
 27. The apparatus according to claim 18,wherein the upstream perimeter of the upper skirt is disposed upstreamof the leaflet frame.
 28. The apparatus according to claim 18, whereinthe lower skirt is shaped to define a plurality of lower-skirt petals,each of the lower-skirt petals extending radially outward and in adownstream direction from the upper skirt.
 29. The apparatus accordingto claim 28, wherein the upper skirt is shaped to define a plurality ofupper-skirt petals, each of the upper-skirt petals extending radiallyoutward and in an upstream direction from lower skirt.
 30. The apparatusaccording to claim 29, wherein the upper-skirt petals arecircumferentially out of phase with respect to the lower-skirt petals.31. The apparatus according to claim 18, wherein each of the leaflets isdisposed within, and secured to, the downstream portion of the leafletframe.
 32. The apparatus according to claim 31, wherein: the downstreamportion of the leaflet frame comprises a plurality of posts, and at eachpost of the plurality of posts, a part of one leaflet of the pluralityof leaflets converges with a part of another leaflet of the plurality ofleaflets, the part of the one leaflet and the part of the other leafletare secured to the post.
 33. The apparatus according to claim 18,further comprising a plurality of curved prong-shaped anchorsdistributed circumferentially around the longitudinal axis.
 34. Theapparatus according to claim 33, wherein all of the curved prong-shapedanchors are entirely disposed downstream of the upper skirt.
 35. Theapparatus according to claim 33, wherein: the prosthetic valve structurecomprises a plurality of metal segments joined at a respective pluralityof joints, the joints facilitating (i) collapsing of the prostheticvalve structure into a collapsed state for transcatheter delivery to theheart, and (ii) expanding of the prosthetic valve structure into adeployed state within the heart, and each of the curved prong-shapedanchors projects from a respective one of the plurality of joints. 36.The apparatus according to claim 35, wherein: at each of the pluralityof joints from which a respective curved prong-shaped anchor of theplurality of curved prong-shaped anchors projects, a first metal segmentof the plurality of segments is joined to a second metal segment of theplurality of segments, and the respective curved prong-shaped anchor isshorter than the first metal segment and is shorter than the secondmetal segment.
 37. The apparatus according to claim 18, furthercomprising a leaflet-frame fabric that is coupled to the leaflet frame.38. The apparatus according to claim 18, wherein the leaflet framecomprises Nitinol.
 39. The apparatus according to claim 18, wherein theprosthetic valve structure is collapsible into a collapsed state fortranscatheter delivery to the heart.
 40. Apparatus for use at a nativeatrioventricular valve of a heart of a subject, the apparatus comprisinga prosthetic valve structure that comprises: a leaflet frame,circumscribing a longitudinal axis of the prosthetic valve structure;prosthetic leaflets, coupled to the leaflet frame, and configured tofacilitate upstream-to-downstream bloodflow longitudinally through theprosthetic valve structure; an upper skirt, having an upstreamperimeter; and a lower skirt, downstream of the upper skirt, and havinga downstream perimeter, wherein: (1) the upper skirt: extends away fromthe lower skirt, in an upstream direction and radially outward towardthe upstream perimeter, and is configured to rest against an atrialsurface of the native atrioventricular valve, (2) the lower skirt:extends away from the upper skirt, in a downstream direction andradially outward toward the downstream perimeter, and is configured torest against a ventricular surface of the native atrioventricular valve,and (3) a downstream portion of each of the prosthetic leaflets isdisposed downstream of at least part of the downstream perimeter of thelower skirt.
 41. The apparatus according to claim 40, wherein: the upperskirt comprises an upper skirt frame, and fabric coupled to the upperskirt frame; and the lower skirt comprises a lower skirt frame, andfabric coupled to the lower skirt frame.
 42. The apparatus according toclaim 41, wherein the lower skirt frame has an outer edge that defines awavy path circumferentially around the longitudinal axis, and that isdisposed radially outward from the leaflet frame.
 43. The apparatusaccording to claim 40, wherein the lower skirt extends from the leafletframe in a manner that defines a space that circumscribes the leafletframe and is disposed between the leaflet frame and the lower skirt. 44.The apparatus according to claim 40, wherein: the prosthetic valvestructure defines a narrowed waist on a plane that is perpendicular tothe longitudinal axis, longitudinally between the upper skirt and thelower skirt; the prosthetic valve structure further comprises joints,distributed circumferentially around the longitudinal axis on the plane;and each of the joints comprises a respective connecting element thatconnects metallic segments of the prosthetic valve structure by beinginserted into a respective hole of the prosthetic valve structure. 45.The apparatus according to claim 40, wherein the upstream perimeter ofthe upper skirt is disposed upstream of the leaflet frame.
 46. Theapparatus according to claim 40, further comprising a plurality ofcurved prong-shaped anchors distributed circumferentially around thelongitudinal axis.
 47. The apparatus according to claim 47, wherein allof the curved prong-shaped anchors are entirely disposed downstream ofthe upper skirt.